This application claims benefit of Japanese Patent Application No. 2001-184242 filed on Jun. 19, 2001, the contents of which are incorporated by the reference.
The present invention relates to AFC (automatic frequency control) circuit.
Heretofore, in digital demodulators of radio receiver systems, AFC circuits for frequency pull-in are well known in the art.
In the prior art AFC circuit, when detecting synchronization data with a fixed sampling frequency with a phase error near 180°, it become impossible to determine whether the frequency is lagging behind or leading, and this point is a pull-in limit point.
As a measure to cope with this, it is conceivable to provide a highly accurate reference oscillator. The provision of such a high accuracy reference oscillator, however, leads to a problem of difficulty in reduction of the size and price of the whole system.